package com.aidong.util;

import java.io.ByteArrayOutputStream;  
import java.io.IOException;  
import java.io.OutputStream;  
        
/** 
  * Base64编码工具类 
  *  
  * @author liufeng  
  * @date 2012-10-11 
  */ 
public class Base64 {  
     private static final char [] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" .toCharArray();  
        
     public static String encode( byte [] data) {  
         int start = 0 ;  
         int len = data.length;  
         StringBuffer buf = new StringBuffer(data.length * 3 / 2 );  
        
         int end = len - 3 ;  
         int i = start;  
         int n = 0 ;  
        
         while (i <= end) {  
             int d = (((( int ) data[i]) & 0x0ff ) << 16 ) | (((( int ) data[i + 1 ]) & 0x0ff ) << 8 ) | ((( int ) data[i + 2 ]) & 0x0ff );  
        
             buf.append(legalChars[(d >> 18 ) & 63 ]);  
             buf.append(legalChars[(d >> 12 ) & 63 ]);  
             buf.append(legalChars[(d >> 6 ) & 63 ]);  
             buf.append(legalChars[d & 63 ]);  
        
             i += 3 ;  
        
             if (n++ >= 14 ) {  
                 n = 0 ;  
                 buf.append( " " );  
             }  
         }  
        
         if (i == start + len - 2 ) {  
             int d = (((( int ) data[i]) & 0x0ff ) << 16 ) | (((( int ) data[i + 1 ]) & 255 ) << 8 );  
        
             buf.append(legalChars[(d >> 18 ) & 63 ]);  
             buf.append(legalChars[(d >> 12 ) & 63 ]);  
             buf.append(legalChars[(d >> 6 ) & 63 ]);  
             buf.append( "=" );  
         } else if (i == start + len - 1 ) {  
             int d = ((( int ) data[i]) & 0x0ff ) << 16 ;  
        
             buf.append(legalChars[(d >> 18 ) & 63 ]);  
             buf.append(legalChars[(d >> 12 ) & 63 ]);  
             buf.append( "==" );  
         }  
        
         return buf.toString();  
     }  
        
     private static int decode( char c) {  
         if (c >= 'A' && c <= 'Z' )  
             return (( int ) c) - 65 ;  
         else if (c >= 'a' && c <= 'z' )  
             return (( int ) c) - 97 + 26 ;  
         else if (c >= '0' && c <= '9' )  
             return (( int ) c) - 48 + 26 + 26 ;  
         else 
             switch (c) {  
             case '+' :  
                 return 62 ;  
             case '/' :  
                 return 63 ;  
             case '=' :  
                 return 0 ;  
             default :  
                 throw new RuntimeException( "unexpected code: " + c);  
             }  
     }  
        
     /** 
      * Decodes the given Base64 encoded String to a new byte array. The byte array holding the decoded data is returned. 
      */ 
        
     public static byte [] decode(String s) {  
        
         ByteArrayOutputStream bos = new ByteArrayOutputStream();  
         try {  
             decode(s, bos);  
         } catch (IOException e) {  
             throw new RuntimeException();  
         }  
         byte [] decodedBytes = bos.toByteArray();  
         try {  
             bos.close();  
             bos = null ;  
         } catch (IOException ex) {  
             System.err.println( "Error while decoding BASE64: " + ex.toString());  
         }  
         return decodedBytes;  
     }  
        
     private static void decode(String s, OutputStream os) throws IOException {  
         int i = 0 ;  
        
         int len = s.length();  
        
         while ( true ) {  
             while (i < len && s.charAt(i) <= ' ' )  
                 i++;  
        
             if (i == len)  
                 break ;  
        
             int tri = (decode(s.charAt(i)) << 18 ) + (decode(s.charAt(i + 1 )) << 12 ) + (decode(s.charAt(i + 2 )) << 6 ) + (decode(s.charAt(i + 3 )));  
        
             os.write((tri >> 16 ) & 255 );  
             if (s.charAt(i + 2 ) == '=' )  
                 break ;  
             os.write((tri >> 8 ) & 255 );  
             if (s.charAt(i + 3 ) == '=' )  
                 break ;  
             os.write(tri & 255 );  
        
             i += 4 ;  
         }  
     }  
} 
